The Low End Mac Mailbag

Running a PowerBook in OS X from Flash Memory, CPU Upgrades and Cache Size, USB and Older Macs, and More

Dan Knight - 2007.05.25

Running OS X from Compact Flash

John Muir writes:

Hi Dan,

Just read your article about running from a Compact Flash card via an IDE adapter. I have a little I could add to your report.

Since last October, I've been running my 12" PowerBook G4 (original 867 MHz model with 640 MB RAM) from an 8 GB CF card in just such an adapter I bought some months before. I'm currently right up to date with OS X 10.4.9 and still have a few gigs free besides having Office 2004 installed and my usual other apps. I'd call the experiment a success, as this is my main machine a lot of the time and has been used daily over that period, but as you found yourself often it's getting there which is the tricky part. If you'd like to hear the full story, I could mail you back on it; it's easily enough for the OS X inclined.

A quick hint: FireWire target disk mode. It's great when you have it and lets me "sand box" on an external drive when trying new things out.

All in all I'm happy with my setup. The silence is truly golden. Eventually I'd like to up the flash card - because as you discovered yourself cards can be "idiosyncratic" shall we say - and Leopard seems the best excuse for that. Apple didn't make these 12" PowerBooks with hard drive replacement in mind, so it's a task I'm well prepared to let wait!


Hi John,

Thanks for the good news about running OS X from flash. I assumed it would work, and I'm glad to hear from someone doing it successfully. Does the PowerBook feel as responsive running from Compact Flash as it did with a hard drive? My PB 1400 seems to wake up faster from sleep when running from flash; how about your 12" PB G4?

I imagine it took some work to trim OS X and your application library to fit on an 8 GB card with room for Office 2004 and work files. If you'd like to share that story, I'd be happy to publish it.


Running Old PowerBooks from Flash Is Very Tempting

Andrew Main writes:


Thanks for this article. For over a decade I've been hoping to see flash memory replace noisy (though that problem's mostly been solved in recent years), unreliable (moving parts wear out) hard disks. Maybe it won't be too long now before flash prices reach rough parity with disks.

I also have a PB 1400 (with a 250 MHz G3 CPU); it was one of the all-time greats, and I keep it around as a Mac OS 8.6/7.6 machine. It has a 2 GB drive in it now; a flash replacement for under $50 is very attractive. And my 'Pismo' PB, which I keep for Mac OS 9 & 10.3 (and to play with Linux) could do nicely with a 16 GB flash drive to replace the 20 GB in it now.

I note Addonics also offers an SATA version of their 2.5" adapter card; I just bought a 160 GB disk for my MacBook Pro for ~ $100, but I'd pay $200 for a 256 GB flash memory card to replace it.

As for older Mac notebooks that use SCSI disks, there may be a possible solution: In the waning days of the SCSI era, Apple was offering replacement 1 GB disks that were actually IDE/ATA disks with an ATA-to-SCSI adapter card attached. I've used one of these to make a 2 GB ATA disk usable as a SCSI drive, and it might work with one of the Addonics adapters. Maybe I'll give it a try when I get around to assembling a PB 180c (another all-time favorite) from the boxes of parts in the corner.

There might also be ATA-to-SCSI adapters for full-size 3.5" disks; I seem to have a dim memory of seeing something like that once. I note Addonics also makes some 3.5" flash to ATA adapters, so there might even be hope for your Mac Plus - or the accelerated (16 MHz!) LC I plan to put together for System 6 (fast and stable - remember?).



First off, I'm jealous of your G3 upgrade. I'd like to acquire one someday for my 1400, and also do some hardware transplants. I have a 133 MHz one with 64 MB of RAM and an internal ethernet card, and I have a 166 MHz one with the superior display. Combined with a G3 upgrade and a WiFi card, it could be a great machine for the classic Mac OS.

I'm updating my review with a link to the SATA adapter, which unfortunately only holds a single CF card. Still a cool device!

I like your thinking. I'd love to have a flash drive for my accelerated Mac Plus, but fiddling with a CF card and some adapters isn't tempting at all. I'll wait for someone else to figure it out first. (And I'd be happy to publish their results here on Low End Mac.)

If you find a source of those ATA-to-SCSI adapters for notebook drives, be sure to let me know.


Testing a Compact Flash Hard Drive

Lee Kilpatrick says:

I enjoyed reading the review of the Addonics CF adaptor for a hard drive replacement, but I was wondering if you tried it in your Power Mac G4? The 1400 is, as you pointed out, not a very modern machine, so maybe the speed was limited by the machine itself, and the G4 would give a better idea of how a flash drive might perform on a more current system. Not sure what speed the ATA bus is in your G4, but it seems like it would almost surely be faster than the 1400.



Thanks for the suggestion, but there are two reasons I didn't try it. First, 2.5" IDE hard drives don't use the same connector as 3.5" hard drives, and I don't have the appropriate adapter. Second, it's a royal pain taking my Power Mac G4 out of my desk and then putting it back in place and getting everything plugged into the right ports (I have some USB 1.1 devices on the internal ports, USB 2.0 on a pair of add-in cards). Besides, it's my production machine, and I'd rather not experiment on it.

I really should pick up a nice Lombard or Pismo some day, as either would make a better testbed for notebook upgrades and allow me to run both the classic Mac OS and OS X. I also have some older G3 and G4 Power Macs I could use as a testbed. I'll check with Addonics about the appropriate adapter.


More to CPU Upgrades than Clock Speed

Glenn Dawes writes:

Hey Dan,

Very nice piece on the MDD upgrades. However, it is old news, but it is nice to have it collected as you have. I have been seriously considering upgrade options for the CPU on my single 1.25 MDD for 2 years now, and I remember when Giga first introduced their upgrades as either 1.25 dual or 1.42 dual. The 1.42 was unstable and hard to get two 7455B to work at 1.42. 1.33 seemed to be a sweet spot, and I suspect they discontinued the dual 1.25 as a result. But my recollection is that the Giga 1.33 is an overclocked 1.25 setup, which shouldn't be a problem, but nice to know. This upgrade is plug and play, since the chipset is the same from stock.

The Sonnet upgrades are new and only about 2-4 months old. They use the 7447A chipset which will require a ROM update to run in any MDD, since the MDD only recognizes the 7455B chipset - also not a problem, since Sonnet provides the software ROM update. This is not plug and play. Also the Sonnet chips have no L3 cache and a 512K L2. All things considered, my discussions with a Sonnet tech indicates that a dual 1.25 stock with 1 MB L3 is very very slightly slower than a dual 1.6 7447A with 512k L2, and the 1.8 is marginally faster overall because of the 1.8, however without the L3 there is some serious bottleneck slow down with the slow 167 MHz [system bus] (say compared to a G5).

Further, Chris Seitz is not entirely correct on the space limitations for a CPU upgrade in a MDD tower. There is plenty of room, and the small size of the heat sink on the Sonnet upgrade has to do with the upgrade being designed to work in an Xserve, which if you remember is very flat. The MDD is roomy, which is why the Giga upgrade has not only a taller heat sink but a large fan on top of that. The Giga upgrade will only work in MDD Macs where there is room, but it will not work in an Xserve, which is based on the same architecture as the MDD (actually vice versa - the MDD is based on the Xserve, but as a tower, not a stackable flat server). You might want to correct that in your article . . . there is room in the MDD . . . lots, and the limitation for upgrades is more about the stability of the architecture rather than absolute space.

That said, if you would like a script of the discussion I had with a Sonnet rep about their upgrades and there performance over a stock 1.25, I can send that to you to publish for your readers. I found it useful, and they might as well. Just let me know if you are interested, and I'll email you the text - it's about 2 pages of detailed information organized as questions followed by answers.

My interpretation from the conversation is the Giga upgrade is a better deal, plug and play, and probably a faster upgrade overall than a 7447 based upgrade. Basically the dual 1.6 Sonnet is equivalent to a dual 1.25 stock, and the 1.8 is about the same as a dual 1.42 stock. So the $499 for the dual Giga 1.33 is right about in the middle for performance, is plug and play without a ROM update to recognize the 7447 chipset, and is faster than the $499 1.6 from Sonnet. All upgrades are duals.

If I were to recommend one or the other upgrade for an MDD owner, I would easily recommend the Giga overall, despite the very slight overclock. The Sonnet 7447 are too expensive for basically the same performance and are not plug and play exactly. Both are good but I would prefer the Giga.



Thanks for sharing your findings. I have no way of determining how much space there is inside my Power Mac G4 when it's closed, but I know the stock CPU module has a pretty large heatsink attached.

It's hard to project how two different upgrades will perform in the same computer. The Giga is a slower CPU with a smaller L2 cache, but it has a large (2 MB per CPU) L3 cache. The Sonnet upgrades clock faster and have a larger L2 cache, a different revision of the G4 CPU, and no L3 cache. I haven't been able to locate any benchmark results that would allow me to compare the two.

The Giga has twice as large a L3 cache as Apple's CPUs, so it would probably hold its own against Apple's 1.42 GHz model. Without a L3 cache, the 1.6 GHz Sonnet could well be slower than the stock 1.42 or Giga's 1.33. Let's hope Bare Feats or someone else has the opportunity to test them.

It's not much of a concern whether an upgrade requires a ROM update, and since speeds are likely to be similar, I'd lean toward the Sonnet 1.6 GHz at $50 less, but there are probably equally valid reasons (L3 cache, for instance) for choosing the Giga Designs upgrade.


G4 Upgrade Questions

Kate writes:

Dear Dan,

After my last emails, I did decide to upgrade my G4 400 MHz Sawtooth. I am adding more RAM and I am looking at Processors. One of the games I have and want to play (Myst V) recommends 1.6 GHz. I have been looking at the Sonnet both in the 1.6 and the 1.8 and then saw the Newer Tech MAXpowr 1.8, which says that it is faster than the others because instead of a 7447, it is a 7448. Whatever that means. It is also $100 more.

My thought is that if it's that much faster, why don't they say it's a 2.0? What is a good choice, and are there ratings for this processor, at least I haven't been able to find any. Next question. In one of your articles you said something about the RAM slowing everything down. Is there a limit to what the processor can do because of the speed of the RAM? And to piggyback on that. It seems that somewhere I read that I could use either the PC100 or PC133 memory sticks, in fact I think I have some PC133 in my machine. Thanks a ton, I love my Mac and love making it last.



There are several different factors that determine how much computing power a CPU has. There's raw clock speed, like 1.8 GHz, which only tells us how fast it can handle data after it's acquired it. Then there are the caches, which act as high speed buffers between main system memory (100 MHz to 167 MHz on G4 Power Macs) and the CPU itself (350 MHz to 2.0 GHz).

The "level 2" (L2) cache is the one closest to the CPU (level 1 is in the CPU itself), and on modern G4s, it runs at the same clock speed as the CPU. The 7447 has a 512 MB L2 cache, while the 7448 has a 1 MB L2 cache. That's twice as big, which means two times as much data is available to the CPU immediately. (Some G4s, such as the PowerPC 7455, only have a 256 MB L2 cache. However, it also supports a level 3 cache, which acts as a large buffer between system memory and the L2 cache.)

To answer your question, "if it's that much faster, why don't they say it's a 2.0?" That's because a CPU's clock speed is an absolute measurement. It doesn't measure performance; it only tells how many times per second the CPU can do something.

In general, the more times per second it can perform a calculation, the better, but the other factor is that it must have data and instructions to work with. If that information isn't in the L1 cache, it has to call for it from the L2 or L3 cache - or even system memory. Each step further away from the L1 cache means a longer delay in waiting for that data to reach the CPU. And while it's starved for data, it's wasting those cycles doing nothing at all.

That's why the caches are so important. The faster the cache, the more quickly the CPU can acquire data from it. The larger the cache, the more data you'll have for the CPU to acquire quickly. Of course, there's a downside to this - otherwise we'd have CPUs with 1 GB L2 caches. It takes a lot of circuitry to double the size of a cache, which increases chip size and cost. That's why every CPU is a compromise of bus speed, core speed, and cache size.

In the end, the 7448 was the pinnacle of G4 design when it comes to the size of the L2 cache. All else being equal (which isn't always the case), a 7448 running at the same speed as a 7447 or 7455 will provide the best performance.

That said, there are other factors at play. While Ubisoft says a 1 GHz G4 and 32 MB of video memory is a minimum requirement for Myst V, Inside Mac Games notes that "users with stock 1.6 GHz G5 desktops have had to turn the game down to low settings to achieve playable performance." The reviewer then goes on to recommend a minimum of a 1.42 GHz G4 and 128 MB of video memory on your graphics card.

Between spending $450-600 for a CPU upgrade and $120-150 for a Radeon 9200, you might want to investigate the performance potential of the $599 Mac mini with its 1.66 GHz Intel Core Duo CPU ($519 refurbished from the Apple Store, when available).


USB Adapter for a PCI Power Mac

Dear Mr. Knight,

I have a Power Mac 7200 which uses a serial port for the printer connection. Could you please tell me if an adapter is made which would convert the serial port to a USB connection so that I could use a new printer. If such an adapter is made, where can I obtain one?

Thank you.

Leo Comrie
Galesburg, MI

Hi neighbor (we're about an hour away in Grand Rapids, MI),

I don't know of an adapter that will convert the Mac's serial port to USB, but there's a simpler solution. Your Power Mac has PCI expansion slots, and there are USB cards that plug into PCI slots that will work with Macs. They generally require Mac OS 8.1 or later, which should run nicely on your 7200. A Google search for "usb pci mac" should give you some good leads.


No Tiger Drivers for Many Lexmark Printers

Responding to advice offered in Getting a Dell Printer to Work with a Mac, John Hatchett writes:


Thanks for the tip! However, Lexmark doesn't seem to have a lot of printers that have "Tiger" drivers. Still, I need to go home and make a visual inspection to see if I can match my printer up to the Lexmark printer. I can try and access it through the built Lexmark Printer sharing function of Tiger.

What do you do with a PowerBook 180?

My boss found one lurking around a science room - and it still works! For a while it hung around the eMac lab, and then I had an inspiring thought. Students signed in and out of the writing center all day, and I spent a lot of my time attempting to enter their handwritten entries into a spreadsheet. (The lack of neat penmanship in current high school students is appalling. I could go on about their inability to read an analog clock, but....)

Eureka! I thought, make the students use the PowerBook 180 to log in and out electronically! The PowerBook runs OS 7.5, and it has a floppy drive. As soon as can install AppleWorks in my new Intel iMac, I should be able to translate the file to something more usable.

There is nothing like using old technology to solve new problems.

John Hatchett


Congratulations on finding a great new use for old technology. System 7.5.3 and the 7.5.5 update are free downloads from Apple, and older versions of ClarisWorks should run just fine, allowing you to use a spreadsheet or database for your information.

Sorry to hear that Lexmark is deficient in Tiger support, as that version of the Mac OS has been current for two years now.


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Dan Knight has been publishing Low End Mac since April 1997. Mailbag columns come from email responses to his Mac Musings, Mac Daniel, Online Tech Journal, and other columns on the site.

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