Since Mid-2002, Apple computers started using DDR SDRAM (Double Data Rate Synchronous Dynamic Random-Access Memory), the first model being an Xserve G4 1.0, shipping with 266 MHz PC-2100 DDR.
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As of September 2025 the latest iteration is DDR5, with DDR6 planned for 2027, and current Apple silicon devices are using LPDDR5X, a low-power version of DDR5.

• RAM sticks aren’t designed to be forward or backward compatible. RAM sticks cannot simply be swapped out for other versions of DDR SDRAM – they will not fit, nor be electrically compatible, nor would they “bong”.
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• Most Macs with removable memory are designed to work with a specific clock speed, or can operate in a range of clock speeds. Depending on the model, your Mac may either:
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  • Effectively manage the clock speed of the installed mismatched RAM (Like a 2011 iMac).
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  • May be far more picky (Like a Power Mac G5), desiring in-spec RAM.
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  • May have Error Correcting Code (ECC) – uses ECC to detect and correct n-bit data corruption in-memory, and produces extra heat (Like a Mac Pro 1,1).

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Original DDR

The first generation was simply known as DDR, but can also be referred to as DDR1 to distinguish it from later generations. It was relatively power hungry compared to modern RAM.
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The very first Mac to carry the first generation of DDR was the Xserve G4 1.0. This rack-mounted PowerPC Macintosh server had a total of 4 RAM slots, allowing up to 2 GB. This Mac originally came out in May 14th 2002, but not all Macs carried this improvement right away.

More devices gained DDR SDRAM in 2003 such as the iBook G4, the 17″ iMac G4 1.0, Power Mac G5, G4 MDD, and others. By 2004, no new Macs remained on PC100/PC133 SDRAM.
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Second-Gen, a.k.a. DDR2

The second generation of DDR SDRAM drops the voltage to 1.8v, ups the prefetch buffer to a 4n Arch, can go up to 8.53 GB/s of bandwidth, and was first seen on the iMac G5 iSight. This generation was meant more for more speed yet better all-around efficiency over the power-hungry first-generation DDR.

The Late 2005 Power Mac G5 models with PowerPC 970MP (Dual Core) CPUs also used DDR2, as well as the Late 2005 15-Inch and 17-Inch DLSD 1.67 Ghz Hi-Res PowerBook G4s.
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• DDR2 carried through much of the Core 2 Duo era of Macs, stretching all the way into 2009. The Mid-2009 non-unibody MacBook 5,2 was the final Mac with DDR2.
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DDR3

Introduced in 2007, the third generation of DDR SDRAM started trickling into Macs the following year. The first Mac to ship with DDR3 was the Unibody MacBook, on October 14th, 2008. It had two slots which could take 1066 MHz PC3-8500 204-pin DDR3 SO-DIMMS.

The 2013 MacBook Air was the first model to ship with LPDDR3 SDRAM. LPDDR SDRAM is a specialized low-power implementation of RAM that’s soldered directly onto the logic board. It differs from DDR3L, which is just a lower voltage version of DDR3 (1.35v) designed for both desktops and laptops.
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Despite this, Macs such as the 2008 – 2011 MacBook Air shipped with standard DDR3 soldered directly onto the logic board as well. DDR3 is roughly a third more energy efficient than DDR2 overall.
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DDR4

Launching sometime in 2014 and later shipping with Mid-2017 iMacs, DDR4 makes major leaps over DDR3. Voltage drops to 1.2v altogether, individual RAM sticks can have up to 128 GB, pin count increased on laptop and desktop modules, and DDR4 stays on an 8n Architecture prefetch buffer.

Macs such as the Mid-2018 15″ MacBook Pro were the first to use LPDDR4. LPDDR4, like its LPDDR3 predecessor, is a low power variant.

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The M1 Mac mini as well as the 13-Inch 2020 MacBook Air, and the 13-Inch 2020 MacBook Pro all use LPDDR4X. LPDDR4X is a low power, high-efficiency version of LPDDR4, which runs at a much lower voltage, at 0.6v.
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DDR5 and LPDDR5X

When Macs made the leap to DDR5 with the M1 Pro Apple Silicon chip, they did so with the mobile-oriented, ultra-specialized, low voltage LPDDR5X. LPDDR5X started showing up in Macs in Late 2021, starting with the M1 Pro MacBook Pros.
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While conventional DDR5 RAM bandwidth spans from 38.5 – 70 GB/s (even more with overclocking), Apple Silicon Macs with any chip that’s not a base M1 chip all have over 100 GB/s of memory bandwidth.
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DDR5 introduces power management ICs directly on the RAM modules, as well as ODECC (On Device Error Correcting Code). On devices such as the M3 Ultra Mac Studio, the memory bandwidth goes all the way up to 819.5 GB/s!
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• See more: Comparison of M-Series Processors on Wikipedia – Apple Silicon – URL