I recently upgraded my macbook from 4G to 8G and wonder if there's a tool to test the quality of new memory. I found memtest 4.22 seems only test about 1G:

$ memtest all 2

Memtest version 4.22 (64-bit)
Copyright (C) 2004 Charles Cazabon
Copyright (C) 2004-2008 Tony Scaminaci (Macintosh port)
Licensed under the GNU General Public License version 2 only

Mac OS X 10.9 (13A603) running in multiuser mode
Memory Page Size: 4096
System has 4 Intel core(s) with SSE
Requested memory: 1048MB (1099390976 bytes)
Available memory: 1048MB (1099390976 bytes)
Allocated memory: 1048MB (1099390976 bytes) at local address 0x0000000101000000
Attempting memory lock... locked successfully
Partitioning memory into 2 comparison buffers...
Buffer A: 524MB (549695488 bytes) starts at local address 0x0000000101000000
Buffer B: 524MB (549695488 bytes) starts at local address 0x0000000121c3b000



I reboot into single user mode as described in this question, and test again. Works better, about 7G memory tested. So I guess the missing 1G is reserved for the graphics card?

  • 1
    The part of memory used, even in single user mode, is the Mac OS X kernel and its I/O buffers.
    – dan
    Dec 17, 2013 at 14:12

2 Answers 2


I suggest you to install memtester for example with MacPorts:

$ port install memtester

and use it:

$ memtester 2G
memtester version 4.3.0 (64-bit)
Copyright (C) 2001-2012 Charles Cazabon.
Licensed under the GNU General Public License version 2 (only).

pagesize is 4096
pagesizemask is 0xfffffffffffff000
want 2048MB (2147483648 bytes)
got  2048MB (2147483648 bytes), trying mlock ...locked.
Loop 1:
  Stuck Address       : ok         
  Random Value        : ok
  Compare XOR         : ok
  Compare SUB         : ok
  Compare MUL         : ok
  Compare DIV         : ok
  Compare OR          : ok
  Compare AND         : ok
  Sequential Increment: ok

To test the whole memory, you need to boot from an external device (USB stick, DVD) with a system that uses the least memory. You can try the Apple Hardware Test by pressing the 'd' key on your keyboard while booting (if it is not working, try with Alt-d to boot the AHT over the Internet). Or you can also try MemTest86 and create a bootable memory stick. I have read some people saying that MemTest86 was better than AHT. However it just happened to me that AHT was able to find a memory failure in my MBP, and MemTest86 did not detect any problem after 4 passes of tests.

  • In newer Mac laptops (post summer 2013), the Apple Hardware Test has been renamed Apple Diagnostics. Similar functionality, and you still hold 'd' at boot time to load it.
    – jvriesem
    Sep 13, 2015 at 1:42

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