Memory and Disc Drive hardware

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Memory and Disc Drive hardware
Working Memory and Permanent Storage
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Memory RAM

• Random Access Memory isnt random at all, its
  just not serial memory
• RAM is the rapid, working, temporary memory of
  the computer (n.b. dont confuse with HDD or
  Flash)

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Memory RAM

• Some RAM types
• Low-power SDRAM
• Double data-rate RAM (DDR RAM)
• DDR2, DDR3, DDR4 (2013?)
• You need a specific type for a particular system

http//www.samsunghub.com/wp-content/uploads/2009/
06/32GB-DDR3-RDIMM.jpg
A 32GB DDR3 RAM module
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RAM packaging

• RAM comes in many formats, including
• 30 / 72 -pin SIMM Very old!
• 168-pin DIMM
• 184-pin DDR
• 240-pin DDR2, DDR3
• 284-pin DDR4 (2013)
• DIL (classic chip shape)
• Flat, square high-density chips
• Speed information may bevisible on the packaging

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RAM Performance

• RAM is usually sold based on the Peak transfer
  rate in megabytes per second
• DDR 1600 - 3200
• DDR2 3200 to 8533
• DDR3 6400 to 17066
• DDR4 double the data rate of DDR3
• Faster RAM is more expensive, as you might expect
  (but obsolete RAM can be expensive, too)

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Latency

• Latency is the time taken from asking for the
  contents of a memory location to actually getting
  the answer
• Several measures
• tCAS to access a column
• tRAD to access a row
• tRP to move from one row to another
• tRAS overall value
• Expressed as a four figure number eg.
• Typical DDR2 5-5-5-15
• DDR3 DDR3-1066 7-7-7-21 DDR3-1333 7-7-7-24

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Cache

• It is possible to buy RAM to run at any given CPU
  speed (2 to 4GHz)
• But cheap mass-market bulk-storage RAM runs at
  around 200 to 800MHz (actual clock speed)
• Typical systems use cache memory built into the
  CPU as a buffer between the CPU and the slow
  RAM
• Cache can be 512KB to 8MB of very fast RAM
• This is a bit like a shop having items on the
  shelves rather than in the warehouse...

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CMOS RAM

• The CMOS RAM is special memory (sometimes a
  separate chip) that needs very little power to
  hold data
• Key system settings are kept in CMOS, e.g.
  hard-drive settings and various motherboard
  settings
• Most older PCs have 256 bytes of CMOS RAM
• Motherboards often have a jumper connection to
  clear it useful when completely reconfiguring a
  system

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ROM

• Read Only Memory can be read but not written to
• The computer needs some instructions when it
  starts up - these are in the BIOS ROM
• Modern BIOS ROMs are so-called flash ROM
• Flash ROMs are a form of EEPROM firmware
• They allow BIOS updates without the need for
  physically swapping the ROMs
• But there can be safety security problems!

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Disc Drive types

• Serial ATA drives started taking over in 2003
  (start at 150MBps, now does 300MBps 2006,
  600MBps 2008)
• SCSI is the Small Computer Systems Interface, a
  smart, fast but more expensive system commonly
  found in PC servers and older Macintosh systems
  (up to 80MBps)
• SCSI has all but vanished at the low and
  mid-price points only has a place with very
  fast drives

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IDE/ATA and SATA
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HDD - Hard Disc Drives

• Change has been rapid over the last twenty years
• Fast mass-storage once meant 80ms access time
  for 10MB hard drives, now 8ms access time and
  over 1000GB (one terabyte) is common
• Matchbox-sized drives for cameras and media
  players can have over 500GB of storage room

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External Storage

• Most external storage devices do not required
  manual installation.
• Uses
• Expanding storage on notebook or PC
• Transporting large amounts of data
• Backing up
• Offline data storage

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External Hard Disk

• 3 different types of interface
• USB
• FireWire
• External SATA
• 3 different sizes
• Full size PC Hard disk size, 3.5 inches width
• Portable size Laptop hard disk size, 2.5 inches
  width
• Pocket size (not popular as they have small
  capacity which can be replaced by Flash memory)

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Flash Memory

• USB flash memory
• 1MB/s (USB 1.1) or up to 60MB/s (USB 2.0)
• Typically 1GB to 64GB of storage
• U3 Smart USB Drive
• Micro SD and Mini SD (HC)
• Use in mobile phones, digital cameras, PDAs
• Up to 64GB of storage
• SD and SDHC
• Use in PDAs, cameras was popular
• Up to 1GB of storage for SD
• 64GB for SDHC

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Solid State Drives

• According to Seagate, 2010 total market for
  notebook HD storage was 69 exabytes (69 billion
  gigabytes) (http//www.pcworld.com/businesscenter/
  article/217883/seagate_solidstate_disks_are_doomed
  _at_least_for_now.html)
• 2011 forecast - a rise to 95 exabytes (Gartner)
• In 2010 the total NAND memory manufactured was 11
  exabytes, only 7 found its way into SSDs
• It would take 250 billion investment in new
  fabrication plants to meet demand in 2011...
• SSDs are not going to take over yet!

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Summary

• We have discussed the basic of different types of
  storage that are used in the PCs
• Memory Performance
• Speed or Bandwidth of memory
• Cache
• CMOS RAM
• ROM
• Disc Drives
• Flash Drives, SSDs

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References, Reading

• DDR Memories Comparison and Overview
• DDR4 SDRAMFrom Wikipedia
• CPU cache From Wikipedia