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Hard Drive Components
Hard Drive Form Factors
Hard Drive History: Notable Drives
Hard Disk Drive Interfaces
Improvement of Hard Drive Characteristics Over Time

Hard Drive Components

A hard disk drive (HDD) is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage and one or more rigid rapidly rotating platters coated with magnetic material.

Some key components of the hard drive are:

  1. An HDD has a spindle motor that spins the disks. This defines the rotational platter speed measured in rpm.
  2. An HDD has an actuator (motor) that positions the read/write head assembly across the spinning disks. This will read or write data to the disks.

    Hard disk drive multi-platter read/write head

    Hard disk drive multi-platter read/write head

  3. HDDs are connected to systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial Attached SCSI) cables. This connects the drive to the computers motherboard or interface card.
  4. A hard drive’s Printed Circuit Board (PCB) connects various components that allow the hard drive to function. If you have ever handled a hard drive, you may recognize the PCB as the green or blue board on the bottom of the device.

IBM 0667 5¼ Inch Hard Disk Drive

On display are the main hard drive components. The PCB was removed as well as the hard drive cover exposing the read/write head and spinning disks.

Year: 1986

Capacity: 70 MB

Interface: EIDE

Platter Size: 5.25″

Description: This drive was in a production server at the School of Computer Science in 1990.

Hard Drive Form Factors

14-Inch-Hard-Disk-Platter-Size 5-1/4-Inch 3-1/2-Inch 2.5-Inch 1.8-Inch 1-Inch 0.85-Inch 24-Inch IBM-0667 Seagate-Barracuda Segate-ST506 Seagate-Cheetah IBM-350 Miniscribe-8425S Hard_Drive_Layout HDD_Interfaces Hard_Drive_Improvement

14 Inch Hard Disk Platter Size

Hard Drive Platters

Hard drive platters in a caddy. They can be dropped into the drive manually and then accessed via the mainframe.

Year: 1961

Description: This 14 inch 200 MB hard disk platter was used at Carleton Universities Computing Services (CCS) Honeywell CP-6 computer system which was in production from 1979-2005.

Name Year Capacity Platter Size Other
Priam 738 336 MB 5.25″ Interface: SCSI 50 PIN
2002 IBM Deskstar 2002 61.4 GB 3.5″ Description: Deskstar-line introduced first 1TB HDD
IBM Travelstar 4GT 1998 4GB 2.5″ Usage: Laptop HDD
Toshiba MK2006GAL 2006/2007 20 GB 1.8″ Usage: Laptop/iPod HDD
Hitachi 3k6 Microdrive 2006/2007 4 GB 1″ Usage: iPod Mini HDD
Toshiba MK2001MTN 2004 4 GB 0.85″ Usage: Cellphone (World’s smallest HDD)

Vintage hard drive ad

Hard Drive History: Notable Drives

Hard drives have been engineered with spin rates as low as 1200 RPM and as high as 15K RPM. In 2022 most common RPM rates, in both laptop and desktop PCs, are between 5400 and 7200 RPM. The most common form factors for HDDs in enterprise systems in 2022 are 2.5-inch, also known as small form factor (SFF), and 3.5-inch, also known as large form factor (LFF).

Name Year Capacity Platter Size Platter Rotation Access Time Weight Interface Description
IBM 350 1956 3.75 MB 24″ 1,200 RPM 600 ms 910 kg The first disk drive
Seagate ST506 1980 5 MB 5.25″ 3,600 RPM 85 ms 2.1 kg First 5¼-inch hard drive
Miniscribe 8425S 1984 20 MB 3.5″ 3,600 RPM 68 ms 0.80 kg XT Early 3.5″ hard drive
Seagate Barracuda ST136475LW 1992 36 GB 3.5″ 7,200 RPM 7.6 ms SCSI-2/3 First 7,200 RPM drive
Seagate Cheetah ST37340SLC 1996 97 GB 3.5″ 10,000 RPM 2.99 ms Ultra3 SCSI First 10,000 RPM drive
Hitachi Deskstar 7K1000 2007 1 TB 3.5″ 7,200 RPM 8.5 ms SATA 3Gb/s First 1 TB 3.5″ hard drive
Western Digital Ultrastar He10 2014 10 TB 3.5″ 7,200 RPM 8.0 ms 0.66 kg SATA First 10 TB hard drive (Helium filled drive)

The IBM 350 disk storage unit, the first disk drive, was announced by IBM as a component of the IBM 305 RAMAC computer system on September 13, 1956. The RAMAC program is generally considered to be the fundamental patent for disk drives.

An IBM 350 Hard Drive being transported

Seagate ST-506

Seagate ST-506 the world’s first 5¼-inch form factor hard disk drive

Hard Disk Drive Interfaces

SCSI: Small Computer System Interface

IDE: Integrated drive Electronics

FC: Fibre Channel

SAS: Serial Attached SCSI

SATA: Serial ATA

Improvements of Hard Drive Characteristics Over Time

Parameter IBM 350 Developed to Improvement
Capacity 3.75 MB 20 TB 5,333,333:1
Physical Volume 1.9 m³ 56,000:1
Weight 910kg 62g 1500:1
 Avg. Access Time 600ms a few milliseconds ~200:1
Price ~$30,000 (2020 dollars) 300,000,000:1
Areal Density 2,000 Bits/Inch² 400,000,000:1