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以今天的标准来看，22G的硬盘还不够塞下几部1080P电影。但是，在互联网形成的初期，当人们还在用MB描述大文件的尺寸时，IBM的这块DASD硬盘的空间足够他们塞下几百万张图片了。

在上世纪80年代末到90年代初，磁带机一直是科学家眼中大容量存储的发展方向。当时，软盘（有3.5英寸和5.25英寸之分，前者普及度最高）已经步入了电子产品的世界中，但是理论上它们的最高读写速度只能达到MB级。正因其小规模容量和读取速度的局限性，用于商业存储解决方案中是绝无可能的。在这种情况下，直接存取存储设备（DASD）应运而生。

DASD与传统的磁带机顺序读写方式有所不同。这种基于磁碟的大容量硬盘能够和现代硬盘一样直接跳转到所读取信息的部分。其中，容量最大的是1989年发售的IBM3390，达到了当时惊人的22.7GB，创下了当时单个直接存取存储设备最高容量的记录。

IBM 3390可以装下最多6块85磅重，3000RPM的硬盘，在两块11英寸的磁之间最大传输速率为4.2MB/秒。咋一听速度似乎没那么快，不过它和当时的竞争对手相比，速度快了40%，延迟也小了15%；与前一代相比，每平方英寸存储容量增大了2倍；同时，每MB的成本降低了将近20%。另外，制造者还利用卤化物密封硬盘，使得IBM 3390更适合银行或者大型公司使用——在宝贵的数据被转移之前，它们存放在硬盘中的安全性有了极大的改善。

当然，安全性越高，价格越贵。3390的零售价在每块9万美元到27.5万美元之间（而且这还是1989年的美元价格）。由于技术要求，安装一台设备至少还需要3块这样的直接存取存储设备。这么看下来，每G数据的成本价至少也得5千美刀了。

Through the late 1980s and early 1990s, magnetic tape drives were the go-to technology for long term storage of large amounts of data. Spinning platter hard drives—such as the ubiquitous 3.5 and 5.25-inch variations—had already been invented but rated to a few MB at most; they lacked the necessary capacity for use as commercial storage solutions. And so Direct Access Storage Devices (DASD) were developed to fill this role.

Unlike tape drives that only allow sequential access to data, these massive, platter-based drives could jump to the necessary information just as modern hard drives do. The largest of these was the IBM 3390, which was unveiled in 1989, and featured a whopping 22.7 GB total capacity—the most ever offered in a single DASD.

The 3390 could accommodate as many as six of the 85-pound, 3,000 RPM hard drives in the video above and transfer data at 4.2MB per second between its 11-inch plates. This might not seem like much, but the 3390 was 40 percent faster with 15 percent less latency than its competitors, offered three times the storage capacity per square foot than its predecessor, the 3380K, and lowered the cost per MB by nearly 20 percent. What's more, was extremely reliable as well thanks to a protective cloud of Halon that permeated the 3390's sealed drives—a feature of great interest to the banks and other large institutions that regularly employed DASDs to hold valuable data until it was transcribed to tape.

This reliability came at a steep price however. The 3390 retailed for between $90,000 and $275,000 apiece (in 1989 dollars) and most setups required at least three DASDs, which works out to about fifty grand per gig.