What was the size of the first IBM hard drive?

The first hard drive produced by IBM was the IBM 350 disk storage unit, introduced in 1956. This groundbreaking device marked IBM’s entrance into the disk storage system market, paving the way for the widespread use of hard disk drives in computers in subsequent decades. But just how large was this inaugural IBM hard drive? What was its storage capacity compared to today’s drives? Let’s take a look at the history and specifications of the IBM 350 disk drive to understand the size and storage of this technology milestone.

The IBM 350 Disk Storage Unit

Prior to 1956, IBM primarily utilized magnetic tape for data storage and retrieval on its early computers. Tape storage had capacity limitations, so IBM engineers began work on developing a random-access disk storage system using spinning platters coated in magnetic material. This led to the release of the IBM 350 disk storage unit, IBM’s first hard disk drive product.

Some key facts about the IBM 350 disk drive:

  • Released in 1956 as a component of the IBM 305 RAMAC computer system
  • Contained 50 24-inch magnetic platters rotating at 1200 RPM
  • Stored 5 million characters (around 5 MB) of data
  • Weighed over a ton and was the size of two large refrigerators
  • Used vacuum tube logic circuits for control
  • Utilized an actuator arm with read/write heads to access data
  • Had an average access time of 600 milliseconds
  • Leased for $3500 per month in 1956 (over $35,000 today)

So in summary, the inaugural IBM 350 hard drive had a capacity of 5 MB and was a large, expensive, but very advanced storage system for its time.

IBM 350 Disk Drive Capacity

To fully grasp the size and capacity of the IBM 350 drive, it helps to look at the specifications:

  • 50 x 24-inch platters providing 200 recording surfaces
  • 100 tracks per platter with 20 sectors per track
  • Each sector held 100 characters (bytes)

Doing the math:

  • 200 surfaces x 100 tracks per surface = 20,000 tracks
  • 20,000 tracks x 20 sectors per track = 400,000 sectors
  • 400,000 sectors x 100 bytes per sector = 40,000,000 bytes

So the full formatted capacity was 40 MB, providing 5 MB of available user storage. While minuscule by today’s standards, 5 MB of data was quite substantial for 1956 computer data storage needs. It was a vast improvement over paper punch cards and magnetic tape systems.

Comparison to Modern Hard Drives

To provide some perspective on how far hard drive technology has advanced, let’s compare the original IBM 350 drive specs to a typical modern desktop HDD:

Specification IBM 350 (1956) Modern 3.5″ Desktop HDD (2020)
Capacity 5 MB 6 TB
Size Refrigerator sized 3.5 inches wide
Weight Over 1 ton 0.37 lbs
Average Seek Time 600 ms 8.6 ms

As the table illustrates, while the IBM 350 was an enormous technological achievement for its era, hard drive capacity and performance has scaled by many orders of magnitude in the over 60 years since its debut.

Some key observations:

  • Capacity has grown by over 1 million times from 5 MB to 6 TB
  • Size has shrunk from refrigerator to palm sized
  • Average seek time has improved by 70 times
  • Despite radical improvements, HDD technology retains some similarities in platter design

So although minuscule by modern standards, the pioneering IBM 350 drive marked the beginning of the hard drive’s prominent role in computer storage and paved the way for the incredible advances we continue to see today.

The IBM 350 Legacy

While the IBM 350 was eventually outdated by technological advances like smaller hard drives, magnetic tape, and in recent decades, solid state drives, its legacy lives on in many ways:

  • Proved high capacity random-access disk storage was viable
  • Established HDDs as a superior storage medium to earlier methods
  • Introduced key HDD technologies like actuators, read/write heads, platters
  • Set the stage for future hard drive development by competitors
  • Spurred the growth of magnetic disk storage through the 1960s and 1970s
  • Inspired later HDD milestones like the IBM 3340 “Winchester” drive

Despite its short time on the market before being replaced by superior technology, the pioneering IBM 350 hard disk drive paved the way for the hard drive revolution that followed it. Its 5 MB capacity was tiny but enormously impactful, proving the possibilities of high-capacity disk storage. This breakthrough launched hard drives as a core computer storage technology – a role they continue to hold over 60 years later.


In summary, the first IBM hard drive – the 1956 IBM 350 disk storage unit – had a capacity of 5 MB. This was an enormous figure for 1956 data storage needs, dwarfing previous magnetic tape and punch card capacities. While minuscule compared to modern multi-terabyte hard drives, the IBM 350’s 5 MB capacity marked a major milestone for disk storage, establishing hard drives as a viable medium for random-access high-capacity storage. Despite its quickly outdated vacuum tube technology, the pioneering IBM 350 paved the way for over sixty years of hard drive development that followed. Its refrigerator-sized frame and 5 MB capacity marked the humble beginnings of hard drives as a core technology that now sees over 1 billion produced annually. Though dwarfed by the storage of our smartphones, we owe a debt to the IBM 350 as the groundbreaking origin of the hard drive’s prominent role in our digital world.

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