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Providing Access to Wasted Memory on Memory Modules

IP.com Disclosure Number: IPCOM000022127D
Publication Date: 2004-Feb-25
Document File: 4 page(s) / 40K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that enables access to unused or additional memory in memory devices on certain ECC devices. Benefits include enabling the system to use the additional memory for different applications.

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Providing Access to Wasted Memory on Memory Modules

Disclosed is a method that enables access to unused or additional memory in memory devices on certain ECC devices. Benefits include enabling the system to use the additional memory for different applications.

Background

Memory modules (i.e. DIMM’s) support ECC by using an additional memory device on the module. Part of the memory on the ECC device, in certain cases, is not used. The following table lists 72-bit wide, single-sided DIMMs that are built using x8, x16, and x32 wide memory devices. One bit of ECC per byte of data is needed to support single bit error correction and double bit detection.

DIMM width in bits

Device width in bits

# of devices + # of ECC devices

ECC device width

ECC Memory wasted

72

x8

8+1

x8

No

72

x16

4+1

x16

Yes-1/2

72

x32

2+1

x32

Yes-3/4th

Table 1

For a 64-bit data bus, 8 bits are needed for the ECC. In all cases an additional device is used to support ECC:

§         For the x8 case, the width of the ECC device is x8, and therefore no ECC memory is wasted.

§         For the x16 case, a wider x16 device is used for ECC to match the memory depth (# of rows). This results in half of the device being used for ECC, and the other half being wasted.

§         For the x32 case 3/4th of the ECC memory is wasted.

Figure 1 shows the case for x16 devices; half the capacity of device D4 is wasted. Figure 2 shows a schematic of a 72 bit DIMM using x16 devices. Half the capacity of device D4 is wasted. Pins I/O [7:0] are no connects. Figure 3 shows the case for x32 devices; three quarters of the...