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如果以较低的时钟速度运行快速 RAM，延迟时间是否会改善？

tag-icon • tag-icon memory performance speed latency ddr
如果以较低的时钟速度运行快速 RAM，延迟时间是否会改善？

我正在购买支持DDR4 2400内存的主板和CPU。

以大致相同的成本，我可以购买以下两种类型的内存：

DDR4 2400 内存时序为 16-16-16-39。DDR4
2666 内存时序为 19-19-19-43。

如果我将 2666 内存安装到 2400 系统中，时序会改善吗？或者即使 2666 内存以 2400 运行，时序也会“锁定”吗？

如果答案取决于所涉及的具体硬件，那么有没有办法（最好在 Linux 中）来确定正在运行的系统中使用的实际时间？

答案1

一般来说，是的...如果内存报告它能够做到这一点，大多数信誉良好的 RAM 确实如此。在大多数情况下，查看 BIOS 应该会告诉您 RAM 的时序。

要查看 Linux 中的内存时序，有几种方法，第一种方法是使用“lshw”，它安装在许多发行版中

acejavelin@BlazingIcicle:~$ sudo lshw -C memory
[sudo] password for acejavelin:          
..,deleted...

      *-bank:1
          description: DIMM DDR4 Synchronous Unbuffered (Unregistered) 3600 MHz (0.3 ns)
          product: CL18-22-22 D4-3600
          vendor: Unknown
          physical id: 1
          serial: 00000000
          slot: DIMM 1
          size: 16GiB
          width: 64 bits
          clock: 3600MHz (0.3ns)
... Deleted...

或者使用 i2c-tools，虽然这个在较新的主板上不太准确，例如使用 A-XMP 的 MSI MPG X570，但它会显示 RAM 支持的所有标准时序......

sudo modprobe eeprom
解码 dimms

结果如下：

Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/0-0052
Guessing DIMM is in                              bank 3

---=== SPD EEPROM Information ===---
EEPROM CRC of bytes 0-125                        OK (0xC408)
# of bytes written to SDRAM EEPROM               512
Total number of bytes in EEPROM                  512
Fundamental Memory type                          DDR4 SDRAM
SPD Revision                                     1.1
Module Type                                      UDIMM
EEPROM CRC of bytes 128-253                      OK (0x58B6)

---=== Memory Characteristics ===---
Maximum module speed                             2666 MHz (PC4-21300)
Size                                             16384 MB
Banks x Rows x Columns x Bits                    16 x 17 x 10 x 64
SDRAM Device Width                               8 bits
Ranks                                            1
AA-RCD-RP-RAS (cycles)                           19-19-19-43
Supported CAS Latencies                          20T, 19T, 18T, 17T, 16T, 15T, 14T, 13T, 12T, 11T, 10T

---=== Timings at Standard Speeds ===---
AA-RCD-RP-RAS (cycles) as DDR4-2666              19-19-19-43
AA-RCD-RP-RAS (cycles) as DDR4-2400              17-17-17-39
AA-RCD-RP-RAS (cycles) as DDR4-2133              15-15-15-35
AA-RCD-RP-RAS (cycles) as DDR4-1866              13-13-13-30
AA-RCD-RP-RAS (cycles) as DDR4-1600              11-11-11-26

---=== Timing Parameters ===---
Minimum Cycle Time (tCKmin)                      0.750 ns
Maximum Cycle Time (tCKmax)                      1.600 ns
Minimum CAS Latency Time (tAA)                   13.750 ns
Minimum RAS to CAS Delay (tRCD)                  13.750 ns
Minimum Row Precharge Delay (tRP)                13.750 ns
Minimum Active to Precharge Delay (tRAS)         32.000 ns
Minimum Active to Auto-Refresh Delay (tRC)       45.750 ns
Minimum Recovery Delay (tRFC1)                   550.000 ns
Minimum Recovery Delay (tRFC2)                   350.000 ns
Minimum Recovery Delay (tRFC4)                   260.000 ns
Minimum Four Activate Window Delay (tFAW)        21.000 ns
Minimum Row Active to Row Active Delay (tRRD_S)  3.000 ns
Minimum Row Active to Row Active Delay (tRRD_L)  4.900 ns
Minimum CAS to CAS Delay (tCCD_L)                5.000 ns
Minimum Write Recovery Time (tWR)                19.500 ns
Minimum Write to Read Time (tWTR_S)              4.500 ns
Minimum Write to Read Time (tWTR_L)              13.000 ns

---=== Other Information ===---
Package Type                                     Monolithic
Maximum Activate Count                           Unlimited
Post Package Repair                              One row per bank group
Soft PPR                                         Supported
Module Nominal Voltage                           1.2 V
Thermal Sensor                                   TSE2004 compliant

---=== Physical Characteristics ===---
Module Height                                    32 mm
Module Thickness                                 2 mm front, 2 mm back
Module Reference Card                            A revision 0

---=== Manufacturer Data ===---
Module Manufacturer                              Undefined
Part Number                                      Undefined

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